Safety solenoid having a permanent magnet latching means



sept. 14, 1965 D. D. MUSGRAVE SAFETY SOLENOID HAVING A PERMANENT MAGNETLATCHING MEANS Filed sept. 24, 196s United States Patent 3,206,656SAFETY SOLENOID HAVING A PERMANENT MAGNET LATCHING MEANS Daniel D.Musgrave, 8201 Caraway St., Cabin John, Md. Filed Sept. 24, 1963, Ser.No. 311,068 Claims. (Cl. 317-172) -This invention relates to a safetysolenoid of the moving plunger type. Such devices are frequently used toeffect mechanical actuation from a distant station which is connected tothe solenoid by electrical conductors. Because of their low cost, easeof installation, and simplicity, solenoids are widely used in industrialand military equipment. The solenoid may provide direct mechanicalactuation or it may be used to control a prime mover. As a result oflong usage and development, solenoids can be expected to functionproperly upon signal when situated in any normal environment.

Equal importance must be placed upon another kind of reliability, thatis, assurance that the unit will not function independent of theoperators willful signal. This is particularly true when the solenoidarms a weapon system or controls a power plant, for in such applicationsinadvertent operation might cause a disastrous accident. It is notintended to limit the utility of the present invention by the aforesaidexamples, fo-r the safety features of this invention can be usedadvantageously in other installations. In any system where the endresult must be carefully controlled, consideration must be given tosafeguards against human error, environmental conditions, andcombinations of circumstances which might result in inadvertentactuation.

The hazards associated with electrically actuated devices are diicult toevade completely, particularly because electrical energy is not normallyvisible and because under some circumstances it can be transmittedwithout a physical conductor. It is usually necessary to specify a lowenergy level for intentional actuation in order to avoid excessive timelag between the signal and the actuation. The constantly increasingusage of electric and electronic equipment provides more and moresources from which electrical energy may be unintentionally introducedinto a solenoid circuit.

Important sources of extraneous electrical energy which are recognizedas particularly dangerous to circuits controlling high-energy devicesare lightning, static changes, galvanic `action and radio-frequencyenergy. Designers also try to make it difficult to accidently introduceelectricity from improper connections of conductors. The radio-frequencyhazard has recently become severe, particularly because modern emitters,such as radar equipment, transmit in a concentrated beam.

The above discussion pertains to typical hazards but is not exhaustive,nor is it intended to be limiting.

In consideration of the aforesaid circumstances, the principal object ofthis invention is to provide a safety solenoid which is relativelyimmune to typical extraneous electricity.

Another object is to provide such a solenoid which does not consumepower when standing by in a safe condition.

Another object is to provide a solenoid so designed that inadvertentchanging of polarity of conductors will not permit unintentionalfunctioning.

Another object is to provide a safety solenoid having a single circuitfor control and actuation, which circuit may be tested for continuitywithout causing the solenoid to function.

These and other objects of the present invention will be apparent uponreference to the following specification,

3,206,656 Patented Sept. 14, 1965 ice taken in connection with theaccompanying drawings, wherein:

FIGURE 1 is a plan View, partly cutaway, of a safety solenoid whichembodies the present invention.

FIGURE 2 is a cross-section taken in the plane indicated by numerals 2-2on FIGURE 1.

FIGURE 3 is a cross-section taken in the plane indicated by numerals 3-3on FIGURE l.

FIGURE 4 is an external view of a portion of the solenoid shown inFIGURE 1, with an additional element added for an alternate.

FIGURES 5, 6, 7, 8 and 9 are schematic views which illustrate thesequence of events in a typical cycle of operation of the safetysolenoid shown in FIGURES 1, 2, vand 3, and the electric input to thecoil during each stage of the cycle.

Referring to FIGURES 1, 2, and 3 there is shown a safety solenoid havinga frame 1, of iron or some other suitable material. Within frame 1 ispositioned a sleeve 3 having discs 5 and 7 encircling it near its ends,to form a bobbin on which is wound a coil 9, of insulated wire. Theconstruction of the typical coil is well-known in the art and need notbe detailed here. The conductor leads of the coil (not shown) areconnected to a source of electricity (not shown) with a polarityreversing switch (not shown) in the circuit.

Slidable in sleeve 3 is plunger 11 which is fabricated of some materialhaving a high magnetic retentivity. Plunger 11 is a permanent magnetwith polarity as indicated. A hole 13 is formed in plunger 11 forattaching linkage (not shown) to a driven or controlled device.

Also formed in plunger 11 is an axial hole 15 into which is inserted anend of a non-magnetic guide rod 17, which projects substantially alongthe main axis of the plunger. Rod 17 may be aixed in hole 15 by anysuitable mechanical means such as by mating threads on the rod and inthe hole. Positioned on rod 17 at a point along its length is ring 19which may be attached to the rod in any convenient manner. Ring 19should preferably be made of non-magnetic material.

Fixed in sleeve 3, with one of its ends contacting frame 1 is iron plug21. Plug 21 is bored axially to permit rod 17 to slide freely in it.Plug 21 is also counterbored to receive the hollow cylindrical end 23 ofa ball retainer 25 which is inserted through a suitable hole formed inframe 1. Retainer 25 has a shoulder 27 which is in contact with frame 1.Suitable mechanical means are provided to rmly fix end 23 in plug 21.

Retainer 25 is bored longitudinally to permit rod 17 to slide therein.That portion of retainer 25 which extends outward from frame 1 is boredto a greater diameter to accommodate ring 19 as it moves with rod 17.The counterbore in retainer 25 is indicated by numeral 29.

Retainer 25 also has a pair of lateral holes 31 and 33 which extend fromits counterbore 29 to its exterior surface 35. Holes 31 and 33 aretapered and have their smallest diameter near surface 35.

Loosely positioned within holes 31 and 33 are balls 37 and 39,respectively. The diameter of balls 37 and 39 is so chosen relative tothe several diameters of holes 31 and 33 that the balls may be insertedin holes 31 and 33 via counterbore 29 but cannot .pass completelythrough the holes, and may protrude slightly outside surface 35. Whenthe balls thus protrude the distance between them, at their exteriorsurfaces, they define a diameter slightly greater than the diameter ofring 19. When the balls do not thus protrude, but are situatedcompletely within their respective holes, the distance between them attheir exterior surfaces is slightly greater than the diameter of rod 17.

Slideable on exterior surface 35 of retainer 25 is hollow cylindricalpermanent magnet 41 the poles of which :are -oriented oppositely tothose of plunger 11. (Expressed in a different way, the poles of magnet41 and plunger 11 which are nearest to one another are of like polarity,in the disclosed embodiment this being S.) The interior bore of magnet41 is of such a diameter that it can slide on the exterior surface 35 ofretainer 25, thereby covering or uncovering holes 31 and 33 according toits position. To prevent it from sliding completely off, retainer 35 hasflange 43 at its outer end to act as a limit stop.

FIGURE 4 shows an alternate arrangement in which a spring 45 isinterposed between magnet 41 and flange 43.

OPERATION The solenoid shown in FIGURE l is mechanically latched againstoperation, which would consist of movement of plunger 11 toward plug 21.The plunger cannot travel toward the plug because ring 19 on rod 17 isengaged with balls 37 and 39, portions of which are in the path oftravel of the ring. If the ring is thrust against the balls as by pushof rod 17 caused by an attempt of plunger 11 to move toward plug 21, acamming effect results, and the balls tend to diverge. In FIGURE l balls37 and 39 are restrained from diverging by magnet 41 which is overridingholes 31 and 33. So long as the balls are prevented from diverging, thesolenoid remains latched.

It will be assumed that the windings of the coil are such that currentin one direction, such as that depicted in FIGURE 5, produces a fieldtending to move plunger 11 and magnet 41 into the field, while currentin the other direction, such as that depicted in FIGURE 6, produces afield tending to move plunger 11 and magnet 41 out of the field. Thephysical principles involved are wellknown and need not be detailedhere. For convenience, we will refer to the current producing a fieldtending to draw the plunger and magnet into the field as a negativecurrent, and that tending to repel the plunger and magnet out of thefield as a positive current.

The control station of the solenoid and the circuit connecting it to thecoil are not shown. The operator at the control station would beprovided with a source of electric current and means to impress it oncoil 9 in the manner hereinafter described. The control station andcircuit could use various devices well-known in the art and need not bedescribed in detail. As mentioned hereinbefore, a pole-changing switchcan be employed.

FIGURE 5 represents schematically the same situation shown in FIGURE l,but coil 9 is energized and the arrows on plunger 11 and below magnet 41show the direction each is tending to move due to the magnetic fieldaround coil 9. The operator at the control station may check circuitcontinuity to coil 9 by impressing a current pulse as depicted in FIGURE5 on the coil. The flow of current around the circuit may be observed bymetering, or otherwise.

When the operator decides to deliberately cause the solenoid to operate,he first unlatches the solenoid by impressing a positive current on coil9 as depicted in FIGURE 6. The magnetic field produced around the coilwill repel both plunger 11 and magnet 41, but the plunger is preventedfrom traveling any appreciable distance by ring 19 on rod 17 which canmove only to the inner end of counterbore 29.

Magnet 41 can move until it strikes flange 43, which is the position itis shown at in FIGURE 6. It will be noted that in this position themagnet no longer covers holes 31 and 33, and therefore balls 37 and 39are not restrained against divergence.

The solenoid is ready for the actuation stroke depicted in FIGURE 7. Theoperator now suddenly reverses the polarity of the current through coil9. The polarity of the magnetic field associated with the coil isthereby reversed, and both plunger 11 and magnet 41 are attracted towardthe coil. In so moving, magnet 41 will tend to again cover holes 31 and33 but it must travel an appreciable distance to do so. Before it canmove this distance plunger 11 has moved rod 17, thereby causing ring 19to cam balls 37 and 39 apart. Plunger 11 continues its stroke until itcontacts plug 21.

As magnet 41 continues to move toward frame 1 it may cam balls 37 and 39together but this will not afiect the operation of the solenoid as ring19 will have already passed the balls. The electrical input to the coilmay now be permitted to fall to Zero as shown by the dashed line on theinput chart of FIGURE 7. Plunger 11 will remain in contact with plug 21,and magnet 41 will remain in contact with frame 1.

When the operator desires to return the solenoid to the status shown inFIGURE l, he impresses a positive current on coil 9 thereby repellingboth plunger 11 and magnet 41 to their limits of travel, previouslyexplained. This condition is shown in FIGURE 8. The current is permittedto fall to zero and magnet 41, being a permanent magnet, is attracted toand .adheres to, frame 1. In so doing, it forces ball-s 37 and 39together, and the balls engage ring 19, thus restoring the solenoid tothe mechanically latched condition.

If it is desired to assure relatching under all conceivable conditions aspring 45 may be interposed between magnet 41 and flange 43 as shown inFIGURE 4. Energy stored in the spring can assist magnet 41 in itsmovement back to the latched position.

If an extraneous electrical current passes through the coil the effectwill depend on the polarity and other characteristics of the current. Adirect current, if of the proper polarity might cause unlatching, but itwill, at the same time, prevent movement of the plunger into the coil.

An extraneous alternating current might cause chattering of magnet 41against frame 1 but the half-cycle time of typical alternating currentsis too brief to permit unlatching.

There is thus disclosed a safety solenoid which requires predeterminedelectrical inputs in a definite sequence to bring about functioning. Itis not intended to limit the invention to any specific purpose for itwill be of utility in a broad range of industrial, military andcommunications devices.

It will be apparent to those skilled in the art that frame 1 may serveas a return for the magnetic field of the solenoid and that plug 21 mayserve as a core for the solenoid. It will also be apparent that ring 19can act as a detent surface to cooperate with balls 37 and 39 which areadapted to function as detents, and that magnet 41 is adapted tofunction as a latch to restrain movement of balls 37 and 39.

I claim:

1. A safety solenoid comprising: an electromagnet having a core andmetallic magnetic field return means; a permanently magnetized plungerslideable relative to said core and normally retained by releasabledetent means at a position away from said core; and a permanentlymagnetized latch having a magnetic axis substantially coincidental withthe magnetic axis of said plunger and having poles oriented oppositelyto the poles of said plunger, and normally juxtaposed and adhering tosaid field return means at a latched position whereat said latch ispositionally adapted for preventing release of said detent means;whereby a current in a predetermined direction through saidelectromagnet will cause said field return means to repel said latchfrom said latched position thereby releasing said detent means whereuponsaid plunger is no longer retained by said detent means at said positionaway from said core, and whereafter a current through said electromagnetin a direction opposite to said predetermined direction will cause saidelectromagnet to attract said plunger toward said core.

2. A safety solenoid comprising: an electromagnet having a core andmetallic magnetic eld return means; a permanently magnetized plungerslideable relative to said core and normally at a position away fromsaid core; a guide axed to said plunger and having a detent surfacethereon; movable detent means on said eld return means adapted at a rstposition for engagement with said detent surface thereby retaining saidplunger at said position away from said core and adapted at a secondposition for disengagement from said detent surface; and a permanentlymagnetized latch having a magnetic axis substantially coincidental withthe magnetic axis of said plunger and having poles oriented oppositelyto the poles of said plunger, and normally juxtaposed and adhering tosaid eld return means at a latched position whereat said latch ispositionally adapted for blocking movement of said detent means fromsaid lirst position to said second position and movable to an unlatchedposition whereat said latch is not blocking said movement of said detentmeans.

3. The safety solenoid set forth in claim 1 further References Citedbythe Examiner UNITED STATES PATENTS 3,040,217 6/62 Conrad 317-191 X3,126,501 3/64 Flora 317-171 X OTHER REFERENCES Schiebl, Germanapplication 1,035,771, printed Aug. 7, 1958.

BERNARD A. GILHANEY, Primary Examiner.

JOHN F. BURNS, Examiner.

1. A SAFETY SOLENOID COMPRISING: AN ELECTROMAGNETIC HAVING A CORE AND METALLIC MAGNETIC FIELD RETURN MEANS; A PERMANENTLY MAGNETIZED PLUNGER SLIDEABLE RELATIVE TO SAID CORE AND NORMALLY RETAINED BY RELEASABLE DETENT MEANS AT A POSITION AWAY FROM SAID CORE; AND A PERMANENTLY MAGNETIZED LATCH HAVING A MAGNETIC AXIS SUBSTANTIALLY COINCIDENTAL WITH THE MAGNETIC AXIS OF SAID PLUNGER AND HAVING POLES ORIENTED OPPOSITELY TO THE POLES OF SAID PLUNGER, AND NORMALLY JUXTAPOSED AND ADHERING TO SAID FIELD RETURN MEANS AT A LATCHED POSITION WHEREAT SAID LATCH IS POSITIONALLY ADAPTED FOR PREVENTING RELEASE OF SAID DETENT 